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101.
We study electronic structures of two-dimensional quantum dots in strong magnetic fields using mean-field density-functional theory and exact diagonalization. Our numerically accurate mean-field solutions show a reconstruction of the uniform-density electron droplet when the magnetic field flux quanta enter one by one the dot in stronger fields. These quanta correspond to repelling vortices forming polygonal clusters inside the dot. We find similar structures in the exact treatment of the problem by constructing a conditional operator for the analysis. We discuss important differences and limitations of the methods used. 相似文献
102.
Campbell P Thayer HL Billowes J Dendooven P Flanagan KT Forest DH Griffith JA Huikari J Jokinen A Moore R Nieminen A Tungate G Zemlyanoi S Aystö J 《Physical review letters》2002,89(8):082501
The first on-line laser spectroscopy of cooled fission fragments is reported. The r ions, produced in uranium fission, were extracted and separated using an ion guide isotope separator. The ions were cooled and bunched for collinear laser spectroscopy by a gas-filled linear Paul trap. New results for nuclear mean-square charge radii, dipole, and quadrupole moments are reported across the N=60 shape change. The mean-square charge radii are found to be almost identical to those of the Sr isotones and previously offered modeling of the radial changes is critically reviewed. 相似文献
103.
Laitinen P Strohm A Huikari J Nieminen A Voss T Grodon C Riihimäki I Kummer M Aystö J Dendooven P Räisänen J Frank W 《Physical review letters》2002,89(8):085902
Self-diffusion of implanted (31)Si and (71)Ge in relaxed Si(0.20)Ge(0.80) layers has been studied in the temperature range 730-950 degrees C by means of a modified radiotracer technique. The temperature dependences of the diffusion coefficients were found to be Arrhenius-type with activation enthalpies of 3.6 eV and 3.5 eV and preexponential factors of 7.5 x 10(-3) m(2) s(-1) and 8.1 x 10(-3) m(2) s(-1) for (31)Si and (71)Ge , respectively. These results suggest that, as in Ge, in Si(0.20)Ge(0.80) both (31)Si and (71)Ge diffuse via a vacancy mechanism. Since in Si(0.20)Ge(0.80) (71)Ge diffuses only slightly faster than (31)Si , in self-diffusion studies on Si-Ge (71)Ge radioisotopes may be used as substitutes for the "uncomfortably" short-lived (31)Si radiotracer atoms. 相似文献
104.
We study a two-electron quantum dot molecule in a magnetic field by the direct diagonalization of the Hamiltonian matrix. The ground states of the molecule with the total spin S = 0 and S = 1 provide a possible realization for a qubit of a quantum computer. Switching between the states is best achieved by changing the magnetic field. Based on an analysis of the wave function, we show that the system consists of composite particles formed by an electron and flux quanta attached to it. This picture can also be used to explain the spin phase diagram. 相似文献
105.
R. Béraud G. Canchel A. Emsallem P. Dendooven J. Huikari W. Huang Y. Wang K. Peräjärvi S. Rinta-Antila A. Jokinen V. S. Kolhinen A. Nieminen H. Penttilä J. Szerypo J. Äystö B. Bruyneel A. Popov 《Hyperfine Interactions》2001,132(1-4):481-486
A new HIGISOL chamber devoted to the study of short-lived products from heavy-ion-induced fusion-evaporation reactions is
proposed. It enables, via the extraction of ions by means of a SPIG (SextuPole rf Ion Guide), to improve the mass resolving
power by a factor 2.5 compared to the previous system using a skimmer-ring assembly. The gas cell was also equiped with an
electric field for faster transportation of recoiling ions to the nozzle where they are ejected with the gas jet. The first
results obtained both with a radioactive α-source and cyclotron beam will be reported.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
106.
A beam cooler for low-energy ion beams was constructed to improve the ion optical properties of radioactive ion beams produced at the IGISOL facility in Jyväskylä. The beam cooler is a buffer gas filled RF-quadrupole. The delay properties and the possibility to accumulate a continuous IGISOL beam and release it in short bunches is discussed. 相似文献
107.
An integer a is said to be regular (modr) if there exists an integer x such that a
2
x≡a (mod r). In this paper we introduce an analogue of Ramanujan’s sum with respect to regular integers (modr) and show that this analogue possesses properties similar to those of the usual Ramanujan’s sum. 相似文献
108.
Danuta Joanna Mozdyniewicz Kaarlo Nieminen Herbert Sixta 《Cellulose (London, England)》2013,20(3):1437-1451
The production of cellulosic man made fibres by the viscose process has been known for more than 120 years now, but still some aspects are not sufficiently understood in detail. The carbohydrates in the pulp are exposed to varying conditions during the manufacturing process. In the first production step of steeping, the strong alkaline treatment leads to undesirable loss reactions of the cellulose. In this study, a comprehensive kinetic model was developed for process simulation of cellulose degradation for the fist time comprising primary and secondary peeling, stopping and alkaline hydrolysis. A total chlorine free bleached beech sulfite pulp was treated with 18 % sodium hydroxide at 40, 50 and 60 °C for time periods up to 80 h. The corresponding reaction rates, activation energies and frequency factors for all reaction steps were calculated. The peeling-off reaction was of great significance for the cellulose yield loss, due to a contribution of the secondary peeling after random chain scission. The moderate decrease of the intrinsic viscosity and the changes in molar mass distribution indicated the validity of the assumption. Further, a reduction of the carbonyl and an increase of the carboxyl groups in the cellulose were observed due to the formation of the stable metasaccharinic acid at the reducing ends of the molecules. The fibre morphology was investigated by SEM measurements. Already short alkaline treatment times favored the dissolution of fibril fragments from the fibre surface leading to a smooth fibre surface. 相似文献
109.
Electron-beam-mediated postsynthesis doping of boron-nitride nanostructures with carbon atoms [Nature (London) 464, 571 (2010); J. Am. Chem. Soc. 132, 13?692 (2010)] was recently demonstrated, thus opening a new way to control the electronic properties of these systems. Using density-functional theory static and dynamic calculations, we show that the substitution process is governed not only by the response of such systems to irradiation, but also by the energetics of the atomic configurations, especially when the system is electrically charged. We suggest using spatially localized electron irradiation for making carbon islands and ribbons embedded into BN sheets. We further study the magnetic and electronic properties of such hybrid nanostructures and show that triangular carbon islands embedded into BN sheets possess magnetic moments, which can be switched on and off by electrically charging the structure. 相似文献
110.
Metal reduction at the interface between two immiscible electrolyte solutions (ITIES) has been studied with scanning electrochemical microscopy (SECM). Metal cations in the aqueous phase are reduced by 7,7,8,8‐tetracyanoquinodimethane anion (TCNQ?) residing in the oil phase, methyl isobutyl ketone (MIBK). TCNQ? is formed at the SECM tip by reducing TCNQ, which results in a positive feedback loop between the tip and the ITIES when an electron is donated to a metal cation. The effect of the Galvani potential difference on the rate of the interfacial electron transfer was investigated, establishing the potential difference either by an additional substrate electrode in the aqueous phase or by an a common ion in both phases. It is shown that the Galvani potential difference as a driving force does enable TCNQ? mediated Cu2+ reduction. Finite element method (FEM) simulations were run to provide information on the reaction kinetics and stoichiometry. 相似文献